1. Technical Field
The present invention relates to a liquid crystal cell, a display device, and a method of fabricating a liquid crystal cell suitably used for injecting liquid crystal into a cell.
2. Discussion of Related Art
There has been a remarkable progress in the popularization of a liquid crystal display device used as an image display device for a personal computer, or other various monitors. The liquid crystal display device of this kind is typically constructed in a manner that a backlight as a sheet light source for illumination is provided in the backside of a liquid crystal cell and, by irradiating a liquid crystal surface having a predetermined expanse to an entirely uniform brightness, an image formed in the liquid crystal surface of the liquid crystal cell is made visible.
Such a liquid crystal cell includes signal and gate lines and the like, a thin film transistor (TFT) having an amorphous silicon layer or the like deposited thereon, a color filter, and so on, which are laminated between two glass substrates.
In fabricating the liquid crystal cell, a substrate having a TFT formed thereon and a substrate having a color filter formed thereon are opposed to each other in a separated state with a predetermined gap, and these two substrates are stuck together by a sealant coated around the opposing surfaces of the substrates. Since a so-called empty cell is formed by sticking together the two substrates in this manner, liquid crystal is injected into this empty cell.
At present, a vacuum injecting method is frequently used to inject liquid crystal into the empty cell. According to this vacuum injecting method, the empty cell is dipped in liquid crystal stored in a vessel in a chamber where a pressure is reduced to a level near a vacuum state. Then, by restoring the pressure inside the chamber to an atmospheric pressure increasedly, the liquid crystal is injected into the empty cell through an inlet formed in the empty cell.
However, even when the liquid crystal is injected by such a conventional method as described above, the injected liquid crystal may involve air to leave bubbles therein in the case where an injection condition is not proper, or there is a shortage of exhaustion or leaving time for the injection in the vacuum injecting method. This situation may cause display failures in the display region of the liquid crystal cell.
To eliminate such bubbles left behind, technologies have been already proposed, as described in the gazettes of Japanese Patent Laid-Open No. Hei 10 (1998)-186384, Japanese Patent Laid-Open No. Hei 11 (1999)-231330, and so on. According to these technologies, bubbles mixed in liquid crystal are pushed out by using a pressure roller to apply pressure to the liquid crystal cell having liquid crystal injected thereto. Even by these technologies, however, the complete removal of bubbles cannot be assured. Therefore, needless to say, there is a demand for the development of technology, which makes it possible to conduct a more efficient and sure process for removing bubbles.
In addition, when the bubbles are pushed out by applying pressure with the pressure roller, a shortage may occur in liquid crystal injected into the liquid crystal cell. However, no measures have been proposed to deal with such a case of shortage so far. This point on the shortage must be taken into consideration for actually conducting pushing-out of bubbles by applying pressure with the pressure roller.
Other problems with regard to the injection of liquid crystal into the empty cell are as follows.
That is, in the foregoing vacuum injecting method, so-called a batch process is carried out, which executes liquid crystal injection by simultaneously inserting a plurality of empty cells into the chamber. In such a batch process, a flow of process is temporarily stopped during reducing pressure (evacuation) inside the chamber and dipping in liquid crystal. Particularly, a capacity of the chamber housing the plurality of empty cells becomes inevitably increased, and it takes a long time, for example, 12 hours or more, to reduce pressure to the predetermined degree of vacuum inside the chamber. These problems interfere with an increase of production efficiency.
In addition, in the vacuum injecting method, as described above, the empty cell is dipped in the liquid crystal in the chamber set in nearly a vacuum state, and then ambient pressure inside the chamber is restored to an atmospheric pressure. Consequently, a large pressure difference occurs between the outside and the inside of the empty cell. In the case where a substrate constituting the empty cell is a plastic substrate, such a pressure difference causes substrate deformation or the like. Thus, under the present conditions, only a glass substrate can be used for the liquid crystal cell fabricated by the vacuum injecting method.
Besides the vacuum injecting method involving the foregoing problems, a so-called dropping method is presented. According to the dropping method, liquid crystal is dropped on one substrate coated with a sealant, and then this substrate is stuck with the other substrate for forming a liquid crystal cell. Even in the dropping method, however, a technology must also be provided to remove bubbles efficiently and surely, and to deal with the shortage of liquid crystal during the removal of the bubbles, when the bubbles are mixed in liquid crystal.
The present invention was made to solve the foregoing technical problems, and the object of the present invention is to provide a liquid crystal cell capable of surely removing bubbles when the bubbles are mixed in liquid crystal injected, a display device, and a method of fabricating a liquid crystal cell.
In order to achieve the foregoing object, a liquid crystal cell of the present invention comprises first and second openings formed on side faces of the liquid crystal cell, which communicate with a space filled with liquid crystal. In the first opening, a gap thereof is larger than a gap between two substrates in a region surrounded by a sealing portion because of a step formed with the region surrounded by the sealing portion by, for example a color filter or the like. Here, the gap between two substrates in the region surrounded by the sealing portion means a gap between electrode surfaces of, for example, a color filter, a TFT, and so on, provided in the both substrates. Because of the first opening, when the bubbles mixed in the liquid crystal during fabricating are pushed out from the first opening, the bubbles remaining with the liquid crystal in the first opening can be prevented from returning to the region surrounded by the sealing portion by the step portion.
A gap of the second opening is substantially equal to the gap in the region surrounded by the sealing portion. Accordingly, when liquid crystal is injected, the liquid crystal is supplied to the second opening, and then a capillary phenomenon (capillarity) causes the liquid crystal to enter the region surrounded by the sealing portion from the second opening. In this case, if the gap of the second opening is set larger than the gap in the region surrounded by the sealing portion, as in the case of the first opening, a step is generated between the second opening and the region surrounded by the sealing portion. This step interferes with smooth liquid crystal injection. On the other hand, by setting the gap of the second opening substantially equal to the gap in the region surrounded by the sealing portion as described above, the liquid crystal can be smoothly injected from the second opening. Such a second opening should preferably be used for replenishing liquid crystal after the bubbles are pushed out from the first opening during fabricating.
The first and second openings may be disposed in the faces of the liquid crystal cell adjacent to each other, or in a corner portion of the liquid crystal cell and in the middle portion of the side face in contact with the corner respectively so as to be separated from each other. The disposition of these first and second openings is decided not only to smoothly discharge bubbles or replenish liquid crystal in the case where a process of pushing-out bubbles is carried out during fabricating, but also to prevent interference with a mechanism of the device for discharging bubbles or replenishing liquid crystal.
A display device of the present invention comprises an outlet for discharging bubbles from liquid crystal in the liquid crystal cell, and a replenishing port bored in the side face of the liquid crystal cell for replenishing the liquid crystal cell with liquid crystal by using a capillary phenomenon are provided. The replenishing port may include an introduction portion formed to be continuous to a color filter, a surface thereof being positioned on the same plane as that of the color filter. In this case, by providing the introduction portion protruding to an outer side of the replenishing port, liquid crystal replenishment based on a capillary phenomenon can be carried out more efficiently. Note that the introduction portion can be made of a material identical to that of the color filter.
A liquid crystal cell of the present invention comprises an opening, wall portions formed on both sides of the opening to reach the outer peripheral end portion of a substrate from a sealing portion, and bubble trapping means. During fabricating, if bubbles are mixed in liquid crystal in a region surrounded by the sealing portion, the bubbles are pushed out to the opening, and then the bubbles enter the opening together with liquid crystal filled in the region surrounded by the sealing portion. Then, by the bubble trapping means provided in the opening, the bubbles mixed in the liquid crystal in the opening can be prevented from returning to the region surrounded by the sealing portion. In this case, as the bubble trapping means, the step portion can be formed in the opening. Alternatively, as the bubble trapping means, a recessed portion can be formed in a portion having the opening formed therein.
A method of fabricating a liquid crystal cell according to the present invention comprises: a first step of obtaining a liquid crystal cell having liquid crystal filled between two substrates; a second step of discharging bubbles mixed in the liquid crystal by pressing the liquid crystal cell; and a third step of replenishing the liquid crystal cell with liquid crystal by using a capillary phenomenon. Accordingly, even when discharging bubbles causes a shortage of liquid crystal in the liquid crystal cell, liquid crystal can be replenished by using the capillary phenomenon.
In the first step, the liquid crystal cell may be obtained by a so-called dropping method, in which liquid crystal is dropped onto one of the substrates coated with a sealant, and then the other substrate is superposed thereon.
The second step is carried out at a temperature in which a viscosity of liquid crystal is lower than the viscosity at a normal temperature, and the sealant is softer than the same at a normal temperature. Accordingly, pushing-out bubbles can be performed more efficiently.
Further, in the second step, if a gap between the two substrates is adjusted by pressing the substrates, then pushing-out bubbles and gap adjustment can be simultaneously carried out. Accordingly, work efficiency can be enhanced.
In the third step, if liquid crystal is replenished from a side in a conveying direction set for conveying the liquid crystal cell, it is possible to prevent a dispenser or the like for replenishing liquid crystal from interfering with a mechanical unit such as a roller or the like for pushing-out bubbles.